Preheat oven to 200°C/400°F/Gas Mark 5. Put all ingredients except sugar and Thai fish sauce into a large ceramic roasting dish. Mix well then place on upper shelf of oven and roast 45 minutes, stirring occasionally. Once the mixture begins to reduce and colour, add sugar and Thai fish sauce and cook a further 30 minutes, stirring twice during this period. The chutney should be thick and the fruit still discernible in shape. (Continue cooking if it is too moist.)
Spoon into sterile glass jars that you’ve had filled with hot water (to prime) and wiped dry. Leave just ½ cm (¼ in) at top of jar. Seal while still hot and leave to cool. Store in the fridge for at least one week before eating. Once opened, make sure you keep refrigerated.